These experiments are designed to study the mechanism of neural excitation in the cochlea, particularly to ascertain the excitatory role of the cochlear microphonics (CM), summating potentials (SP), and the endocochlear potential (EP). This will be accomplished by simultaneously recording the cochlear potentials and the neural responses of single fibers that originate in the turn of the guinea pig cochlea where the cochlear potentials are measured. The potentials will be modified by the application of extrinsic current or low-frequency acoustic masking, and the changes in the EP, CM and SP will be quantitatively compared with the changes in the neural responses. These data will be used to elucidate the role of and the interaction between the inner and outer hair cells. Comparative studies will be made on the neural excitation process in the hair cell system of the lateral line organ of the African clawed toad Xenopus laevis. The effects of electric potentials upon spontaneous and evoked activity and the role of the cupula will be investigated. Theoretical modeling of cochlear function incorporating experimental data will complement the experimental studies.